1. Field of the Invention
The present invention relates to a process and an apparatus for forming ball bumps on the inner leads of a film carrier, the electrode pads of a semiconductor chip, the electrode pads of a printed circuit board, the electrode pads of a flexible circuit board, and the like.
The present invention also relates to a process and an apparatus for removing excess balls from an arrangement plate on which small balls for forming the bumps are held and arranged.
2. Description of the Related Art
The known bumps formed on the electrode pads of an semiconductor chip include wafer bumps and stud bumps.
The wafer bumps are formed on the electrode pads of semiconductor devices fabricated on a semiconductor wafer and not yet cut into chips, by first forming a barrier metal coating on the electrode pads, and then forming a gold or other metal bump on the barrier metal by plating.
The wafer bump has the problems of an increase in the number of the process steps, a reduction in the production yield of the semiconductor devices, and an unacceptable cost particularly when producing many types in small amounts.
The stud bumps are formed on the electrode pads of semiconductor chips by first ball-bonding the pads in the same manner as in the first step of the wire bonding process, and then cutting the bonded wire in its neck to leave a bump on the pad.
The stud bumps have problems in that the cut bumps have pointed tops with uneven heights causing poor reliability and that much process time is required because the bumps are formed pin by pin.
Another known process forms a transferred bump by first growing bumps on a substrate by plating, and then transferring the bumps onto the inner leads of a film carrier. The bumps formed by plating have a semispherical shape providing a bump width greater than a required bump height, and is not suitable for bonding at a small pitch of less than 100 .mu.m.
To solve the above-mentioned problems, a process was proposed to form bumps by transferring small metal balls onto the inner leads.
This process has also a problem in that much time is required in arranging balls one by one on a bonding stage in positions corresponding to positions of the inner leads.
There is also a problem in that, during arranging small metal balls on an arrangement baseplate, excess balls are undesirably adhered to the baseplate or other balls due to electrostatic interaction, etc. Although such excess balls must be thoroughly removed from the baseplate, this is very difficult because the metal balls are very small in size (100 .mu.m or less) and great in number.
U.S. Pat. Nos. 4,332,341 and 5,284,287 disclose a method of attracting small balls to positions corresponding to positions of electrode pads of a semiconductor chip. These patents do not disclose the use of vibration for causing the balls to jump up or removing excess balls. These patents use a small solder ball only.
U.S. Pat. No. 4,462,534 disclose a method of attracting small balls to positions corresponding to positions of electrode pads of a semiconductor chip and a method of causing small balls to jump up for the attraction thereof. This patent does not disclose the use of vibration to remove excess balls. The disclosed small balls are solder balls and are bonded to the head of a connector pin.